Conventionally, an ink jet head used for an ink jet type of printer or the like includes a plurality of pressure chambers which accommodate ink, nozzle plates provided to one end side of each of the pressure chambers and a plurality of piezoelectric actuators provided corresponding to each of the pressure chambers. A plurality of nozzles for discharging ink drops which correspond to each of the pressure chambers are formed on the nozzle plates.
When the piezoelectric actuators are driven, pressure oscillation is applied to the pressure chambers corresponding to the actuators. Due to the pressure oscillation, the volume inside the pressure chamber is changed and the ink drops are discharged from the nozzles corresponding to the pressure chambers. The ink drops are landed on a recording medium such as a recording sheet and dots are formed on the recording medium. As such dots are consecutively formed, characters, images or the like on the basis of image data are printed on the recording medium.
In such an ink jet head, when the ink drop is discharged from the nozzle, there is a case where fine droplets which are incidental to main droplets are discharged. Such fine droplets are called satellites. Since the flying speed of the satellite is slow, the satellites are separated from the main droplets and are landed on the recording medium. As a result, degradation in a printing quality such as printing unevenness or ghosting occurs.
The occurrence of the satellite can be prevented by making a driving voltage of the piezoelectric actuator be low. Since when the driving voltage is low, the discharge speed of the main droplets is slow, the satellites do not occur. However, when the discharge speed of the main droplets is slow, stability in discharging of the ink drops is impaired. Therefore, there is concern that the printing quality may be lowered.